Superabsorbent, freeze dried hydrogels for medical applications

ABSTRACT

Methods are provided for making freeze dried hydrogel and structures therefrom that may be introduced into a patient&#39;s body for medical applications. Precursor components are combined to initiate crosslinking. The combined precursor components are placed in a chilled tray, and allowed to crosslink to a desired level of complete crosslinking before and/or after being placed onto the tray. The partially crosslinked hydrogel is frozen and freeze dried. After freeze drying, the hydrogel is conditioned to substantially complete crosslinking, and formed into one or more structures, e.g., plugs, hemostatic, or other medical devices. For example, the hydrogel may be cut, machined, rolled, folded, compressed, and/or cored into that may be loaded into delivery devices that may be introduced into a body to implant or otherwise deliver the structures into the body, e.g., to seal a puncture or other passage through tissue.

This application claims benefit of provisional application Ser. No.60/743,944, filed Mar. 29, 2006, the entire disclosure of which isexpressly incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to hydrogel materials andmethods for making such materials, and, more particularly to freezedried hydrogel materials, methods for making such materials, methods forforming such materials into devices or structures for medicalapplications and/or for introducing such devices or structures into abody, and to devices and methods for delivering such materials into abody, e.g., to line and/or seal punctures, body lumens, or otherpassages in a body.

BACKGROUND

Hydrogels are materials that absorb solvents (such as water), undergorapid swelling without discernible dissolution, and maintainthree-dimensional networks capable of reversible deformation. Hydrogelsmay be uncrosslinked or crosslinked. Uncrosslinked hydrogels are able toabsorb water but do not dissolve due to the presence of hydrophobic andhydrophilic regions.

SUMMARY OF THE INVENTION

The present invention is directed to hydrogel materials and methods formaking such materials. More particularly, the present invention isdirected to methods for making superabsorbent and/or freeze driedhydrogel materials, and to forming such materials into devices orstructures for introduction into a body. In addition, the presentinvention is directed to devices and methods for delivering suchmaterials into a patient's body, e.g., to line and/or seal punctures,body lumens, or other passages in a body.

In accordance with one embodiment, a superabsorbent biodegradablehydrogel is provided, which may be formed by crosslinking precursorcomponents. The hydrogel may be formed by a process including freezedrying or “lyophilizing” the hydrogel before crosslinking is complete.The hydrogel may be crosslinked in an aqueous phase, e.g., by covalentcrosslinking. In exemplary embodiments, the polymerization mechanismsused may be electrophilic-nucleophilic or free radical initiated. Thehydrogel may be degradable when implanted in tissue or otherwise withina body, e.g., by hydrolysis, or substantially non-degradable. In oneembodiment, the hydrogel comprises at least one macromolecular and/orpolymeric species, e.g., one or more poly-ethylene glycol (PEG) basedmolecules, a protein, or polysaccharide. For example, a highly branchedactive PEG precursor may be mixed with an oligopeptide with two or morelysine groups, e.g., di-, tri-, or tetra-lysine, to form the hydrogel.

In accordance with yet another embodiment, a method is provided formaking freeze dried hydrogel that includes combining precursorcomponents to initiate crosslinking of the precursor components to forma hydrogel, freezing the hydrogel when a desired percentage of completecrosslinking is achieved, freeze drying the hydrogel until a desiredamount of moisture is removed from the hydrogel, and forming thehydrogel into one or more structures. In one embodiment, the hydrogelmay be partially crosslinked before freezing, and crosslinking may becompleted after freeze drying, e.g., by one or more conditioning stepsor processes. In another embodiment, the hydrogel may be partiallycrosslinked before freezing, and crosslinking may be completed duringfreeze drying. In still another embodiment, crosslinking may becompleted after freeze drying and/or conditioning.

In accordance with still another embodiment, a method is provided formaking hydrogel that includes forming a mixture by combining precursorcomponents to initiate crosslinking of the precursor components to forma hydrogel. The combined precursor components, mixture, and/or hydrogelmay be placed onto a tray or other container chilled to a predeterminedchilled temperature, e.g., below the freezing point of the combinedprecursor components. The combined precursor components or mixture maybe allowed to crosslink before and/or after being placed on thecontainer.

The hydrogel may be frozen in the container, e.g., by exposing thehydrogel and/or container to a freezing temperature below the freezingpoint of the combined precursor components for a predetermined freezingduration. The hydrogel may be frozen when a predetermined percentage ofcomplete crosslinking is achieved, e.g., less than one hundred percentcomplete. As used herein, “complete crosslinking” is defined as havingoccurred after sufficient time has elapsed at which the hydrogel hassubstantially no unreacted reactive ester end groups that can enablefurther crosslinking.

The frozen hydrogel may then be freeze dried until a desired amount ofmoisture is removed from the hydrogel. Freeze drying may be completed insingle or multiple successive stages, e.g., including different and/orvariable freeze drying temperatures and/or vacuum pressures. Afterfreeze drying, the hydrogel may be formed into one or more structures.For example, the hydrogel may be rolled, folded, compressed, cored,and/or machined into the one or more structures.

Optionally, before its intended medical use, the hydrogel may beconditioned after freeze drying, e.g., before or after being formed intoone or more structures. Conditioning the hydrogel may include one ormore stages of exposing the hydrogel to a controlled temperature and/orhumidity environment for a predetermined duration, drying the hydrogelusing heat, exposing the hydrogel to a controlled gas environment for apredetermined duration, exposing the hydrogel to an aerosolized buffersolution for a predetermined duration, and/or dessicating the hydrogel.The hydrogel may be conditioned during a single stage or during multiplesuccessive stages, e.g., to achieve one or more desired performancecharacteristics for the final structure(s). In one embodiment,crosslinking of the hydrogel may be completed during the one or morestages of conditioning, e.g., such that the final hydrogel is fullycrosslinked to the extent that the hydrogel no longer has a substantialamount of unreacted ester end groups available for further crosslinking.

Varying the degree of crosslinking in the hydrogel at the time offreezing may allow adjustment of the overall morphology of themacroporous network formed after freeze drying when processing thecomposition. Therefore, partially crosslinking hydrogels before freezedrying may provide various advantages. For example, the pore size, porequantity, pore distribution, density, and/or physical structure of thepolymer network formed after freeze drying a partially crosslinkedhydrogel are parameters that may be optimized to suit specificrequirements or applications. Manipulation of these parameters bypartially crosslinking the hydrogel before freezing may enable thecontrol of performance or functionally desired material properties.These properties may include, but are not limited to, tensile strength,compressive modulus, shear strength, creep resistance, stressrelaxation, rate of hydrogel swelling, and/or magnitude of hydrogelswelling. In one embodiment, a low to moderate amount of crosslinking atthe time of freezing the hydrogel may yield a low to moderate density,softer, more flexible macroporous polymer network capable of rapid,higher magnitude swelling upon exposure to an aqueous environment. Inanother embodiment, a moderate to high amount of crosslinking at thetime of freezing the hydrogel may yield a moderate to high density,stiffer porous or microporous polymer network capable of gradual, lowermagnitude swelling upon exposure to an aqueous environment. These typesof materials may be desirable and advantageous for use in variousmedical applications. Further, adjustment or variation of the degree ofcrosslinking at the time of freezing may facilitate fabrication and/orprocessing of compositions with inherent performance capabilitiesadapted or tailored to provide desired material properties and tofulfill desired performance requirements of individual medicalapplications.

Other aspects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are flowcharts, showing exemplary methods for making freezedried hydrogel.

FIG. 4 is a perspective view of an exemplary structure that may beformed from a freeze dried hydrogel.

FIG. 5 is a perspective view of an exemplary delivery device fordelivering a structure, such as that shown in FIG. 4, into a patient'sbody.

DETAILED DESCRIPTION

Turning to the drawings, FIGS. 1-3 show an exemplary method for makingfreeze dried hydrogel and/or for forming one or more structures fromfreeze dried hydrogel material that may be introduced into a body.Generally, the hydrogel may be a superabsorbent and/or biodegradablehydrogel formed using one or more of the processes described elsewhereherein. The hydrogel may be implanted or otherwise delivered into apatient's body, e.g., within tissue, a body lumen, or other locationsuch that the hydrogel is exposed to bodily fluids or other aqueousenvironment, as described further elsewhere herein. As used herein,“superabsorbent” defines a hydrogel that rapidly absorbs fluid whenexposed to an aqueous environment, e.g., that undergoes between aboutfive hundred and three thousand percent (500-3000%) mass increase (wetweight gain v. dry weight) due to fluid absorption within about five tosixty (5-60) seconds of exposure to whole blood.

The hydrogel made using the methods described herein may have a densitybetween about 0.05 and 0.30 grams per cubic centimeter (g/cc). Density,along with the precursor components and/or other process parameters, mayaffect one or more properties of the hydrogel material, e.g., rate ofswelling, magnitude of swelling, compressive modulus, and the like. Forexample, the hydrogel may rapidly swell when exposed to an aqueousenvironment, e.g., swelling between about five hundred and threethousand percent (500-3000%) of the initial mass within about five tosixty (5-60) seconds (“rate of swelling”). In addition or alternatively,the hydrogel may expand between about five and fifty (5-50) times involume from its dehydrated state after being formed to its fullyhydrated state (“magnitude of swelling”). Once hydrated, the hydrogelmay be absorbed or otherwise degrade within the body over a period oftime, e.g., between about one and ninety (1-90) days or between aboutfive and sixty (5-60) days. Alternatively, the hydrogel may besubstantially non-degradable, i.e., may not substantially degrade withinone or two years in a physiological environment.

The hydrogel formed using the materials and methods described herein mayconstitute a macroporous network, a microporous network or “foam,” i.e.,a two-phase solid-gas system that includes a solid lattice of materialthat is substantially continuous through the hydrogel. The gas phase(e.g., air) may be distributed substantially evenly through the latticein voids or “pores.” The foam may be “open-cell,” i.e., the pores mayinclude openings allowing fluid communication from one pore to anotherthrough the lattice defining the pores.

As shown in FIG. 1, a method for making a superabsorbent, biodegradablehydrogel, such as those described herein, generally includes threesteps: combining two or more precursor materials to initiate creation ofhydrogel material (step 110), freeze drying the hydrogel material (step120), and forming the hydrogel material into one or more structures(step 130). The resulting structure(s) may subsequently be introducedinto a patient's body, e.g., into a puncture, body lumen, or otherpassage through tissue, as described further below. Although the stepsor substeps of the exemplary methods are described herein as beingperformed in a particular order, the steps may be provided in differentsequences than those described.

Turning to FIG. 2, an exemplary method is shown for combining precursormaterials, e.g., during step 110 of the method of FIG. 1. Initially, atstep 112, polymer components may be provided in powder form, e.g.,premanufactured by a supplier. In exemplary embodiments, the polymercomponents may include poly-ethyleneglycol (PEG) based molecules withreactive endgroups, polypeptides, etc. The reactive endgroups mayencompass any set of chemical groups that may form a bond underspecified environmental conditions, such as amine and/or ester endgroups. Multiple types of base polymer (linear PEG of varying molecularweights, star PEG with varying numbers of arms and molecular weights,etc.) may be used.

In an exemplary embodiment, the powder components may simply be a two(2) part system. One example of such a system may include a singlePEG-nucleophile and a single PEG-electrophile. The system may includeformulations, such as those disclosed in U.S. Pat. Nos. 6,566,406 or7,009,034, the entire disclosures of which are expressly incorporated byreference herein to the extent that they do not contradict what isexplicitly disclosed herein. Examples of a suitable system may include acombination of branched electrophilic PEGs and one or more di-, tri-, ortetra-lysines, which have amine functional groups.

For instance, the system may include a first electrophilic precursor anda second nucleophilic precursor, such that the two precursors may bereacted with each other to form a crosslinked hydrogel. For example, aprecursor may be a multi-armed PEG (e.g., with two to twelve (2-12)arms) with electrophilic or nucleophilic functional groups. Precursorweights may range significantly depending upon intended properties,e.g., with arms in the range of about five to one hundred kiloDaltons(5-100 kDa). Examples of electrophilic functional groups aresuccinimidyl glutarate (SG),carboxymethyl-hydroxybutyrate-N-hydroxysuccinimidyl (CM-HBA-NS),N-hydroxysuccinimides, maleimides, and succinimidyl esters. Examples ofnucleophilic functional groups are amines and thiols.

The precursors may be chosen to include groups biodegradable byhydrolysis upon exposure to aqueous solution and/or by targetedenzymatic degradation by incorporating amino acid sequences intended tobe degraded by enzymes relevant to the site of hydrogel application,e.g., collagenases. Examples of hydrolytically degradable groups areesters.

Alternatively, the powder components may be more complicated, i.e.,including more than two powder components, e.g., a four (4) part systemincluding a PEG-amine, a polypeptide, a low molecular weight PEG-ester,and a high molecular weight PEG-ester. Any combination of polymercomponents that may form a hydrogel may be provided for the initialpolymer components.

At step 112, the powder components are individually weighed to a massintended to give a desired percentage of solid polymeric material in thefinal hydrogel (after the powders are reconstituted and mixed together).For example, the powder components may be measured from a bulk containerand placed into individual bottles or other containers. Alternatively,the powder components may be provided pre-measured to the desired massesin individual containers provided by the manufacturer.

At step 114, one or more buffer solutions may also be provided. Forexample, a specific buffer solution may be fabricated to facilitate theuse of each of the individual polymer components, such as thosedescribed above. In exemplary embodiments, the buffer solutions mayinclude a borate buffer (e.g., for an amine polymer powder component)and/or a phosphate buffer (e.g., for an ester polymer powder component).

The buffer solutions may be measured from one or more bulk containers ormay be provided in individual containers, e.g., in an amount having apredetermined ratio with the amount of powder components correspondingto the respective buffer solutions. The buffering agent, molarity, andpH of each of the buffer solutions may be adjusted to achieve a desiredgelation time (i.e., full crosslinking time) when the reconstitutedpolymer solutions are combined.

At step 116, the powder components may be reconstituted with the buffersolutions to create precursor solutions. In particular, each of thepowder components may be reconstituted with their respective buffersolutions and stored in individual containers. For example, each of thebuffer solutions may be poured into the respective containers includingthe corresponding powder components. The containers may then be shakenor otherwise mixed to substantially dissolve the powder components inthe buffer solutions. Additional information on components for precursorsolutions and methods for making them may be found in U.S. Pat. Nos.6,152,943 and 6,606,294, the entire disclosures of which are expresslyincorporated by reference herein.

Depending upon the compounds used for the powder components and buffersolutions, the reconstitution may be completed in advance of the balanceof the process or immediately before completing the process. Forexample, some precursor solutions may remain substantially stable for anextended period of time after the powder components are reconstituted.Thus, such precursor solutions may be prepared in advance of completingthe hydrogel process, e.g., hours or even days in advance. Conversely,other precursor solutions, such as those including PEG-esters, may needto be reconstituted immediately before use, because of the hydrolyticnature of PEG-esters, e.g., about one minute before completing thehydrogel process.

At step 118, after each of the precursor solutions are reconstituted,they may be combined together in a single container. As they arecombined or after being combined, they may be thoroughly mixed toinitiate a crosslinking reaction and creation of hydrogel material. Themethod of mixing may be chosen according to the types of polymer usedand/or the total volume of precursor solutions used. For example, arelatively small volume of non-foaming material may be mixed using acentrifuge or vortex machine, which mixes the solutions with vibrationalagitation. Alternatively, a large volume of precursor solutions may bemixed using a stir plate or other type of non-agitating mixing. Activemixing may be maintained for a predetermined mixing time, e.g., betweenabout ten and sixty (10-60) seconds, to ensure that the combinedprecursor solutions are sufficiently mixed together.

Next, at step 119, the combined precursor solutions may be allowed tosit for a predetermined crosslinking duration, e.g., to allow thecombined precursor solutions to at least partially crosslink.

In exemplary embodiments, the predetermined crosslinking duration may bebetween about half to two-and-a-half (0.5-2.5) minutes for a polymersolution with a full crosslinking time of about four to eight (4-8)minutes. This step may allow the combined precursor solutions tocrosslink to a desired percentage of complete crosslinking beforeinitiating the freeze drying process, e.g., between about one and ninetynine percent (1-99%), including about one to fifteen percent (1-15%),about five to twenty percent (5-20%), about ten to thirty percent(10-30%), about fifteen to forty percent (15-40%), about twenty to sixtypercent (20-60%), about forty to eighty percent (40-80%), about fifty toninety percent (50-90%), and sixty to ninety-nine (60-99%), of fullcrosslinking.

In one embodiment, the combined precursor solutions may be poured into achilled tray or other container, as described above, and allowed to sitat substantially ambient temperatures. Alternatively, the tray may bemaintained at the predetermined chill temperature, e.g., by placing thetray with the combined precursor materials therein in the freeze dryingmachine or a plate set at the predetermined chill temperature (butremaining at substantially ambient pressures). As the combined precursorsolutions cool, the rate of crosslinking may slow and/or cease at adesired percentage before complete crosslinking has occurred.

In a further alternative, the tray may be initially provided at ambienttemperature, and the combined precursor solutions may be allowed to sitat substantially ambient temperatures for the predetermined crosslinkingduration or placed within the freeze drying machine or on a plate set ata desired temperature. In yet another alternative, the combinedprecursor solutions may be allowed to crosslink for the predeterminedcrosslinking duration before being poured onto the tray (which may ormay not be chilled, as described above).

Returning to FIG. 1, once the precursor solutions are adequately mixedand/or at least partially crosslinked, the resulting hydrogel materialmay be freeze dried, at step 120, e.g., in a freeze drying machine. Thefreeze drying machine may be a conventional device including a chambercapable of being maintained at one or more desired temperatures and/orvacuum pressures for one or more desired periods of time. If the freezedrying process includes multiple sequential stages, i.e., each stagehaving a predetermined temperature, pressure, and/or duration, which maybe controlled manually or preprogrammed into the freeze drying machine.

Turning to FIG. 3, an exemplary method is shown for freeze drying thecombined precursor solutions and/or hydrogel material. Initially, atstep 122, a freeze tray may be provided at a predetermined chilltemperature. The predetermined chill temperature may be selected toprovide a desired rate of cooling of the combined precursor solutions,e.g., between about negative twenty to seventy degrees Celsius (−20 to−70° C.). In an exemplary embodiment, the tray may be chilled to atemperature substantially equivalent to the initial freeze dryingtemperature, e.g., not warmer than about negative forty degrees Celsius(−40° C.). For example, the tray may be chilled at the chosenpredetermined temperature by simply placing the tray on the freezedrying machine shelf for sufficient time to allow the tray to attain thefreeze drying temperature of the freeze drying machine. Alternatively,the tray may be pre-chilled in a freezer, refrigerator, on atemperature-controlled plate, or other equipment.

At step 224, the combined precursor solutions and/or hydrogel materialmay be poured onto the tray. The tray may have any desired shapeselected to provide a final shape for the hydrogel material that is tobe formed into the one or more structures. For example, the tray maysimply be a flat tray, e.g., having a round, rectangular, square, orother geometric shape. When the combined precursor solutions are pouredonto the tray, they may assume a substantially uniform thickness acrossthe bottom of the tray, e.g., between about one and twenty fivemillimeters (1-25 mm). Alternatively, the tray may include one or morerecesses to create a predetermined varied thickness or three-dimensionalconfiguration for the combined precursor solutions and/or final hydrogelmaterial. In a further alternative, the tray may include multiplecavities into which the combined precursor solutions may be poured tocreate multiple structures onto the tray that are substantially isolatedfrom one another.

Optionally, the tray may include one or more surface coatings, e.g., tofacilitate removal of the hydrogel material from the tray before orafter being formed into one or more structures, as described below. Forexample, surface coatings that are hydrophobic may be useful for thispurpose, such as Teflon, silicone, Parylene, and the like.

In addition, the tray material (e.g., steel, aluminum, plastic, glass,etc.) may be selected to achieve desired process parameters andmanufacturability. For example, an aluminum tray may cool quickly andhas a high rate of heat transfer, while a Teflon tray may remainrelatively unaffected by sudden changes in temperature. The tray designmay include flanges, radiator like fins or other such features (notshown) that act as heat sinks to dissipate the heat of the liquidsolution into the cold environment. Thus, the material and/or traydesign may be selected to slow or accelerate chilling of the combinedprecursor solutions. In an alternative embodiment, the tray may beprovided at substantially ambient temperatures when the combinedprecursor solutions are poured onto the tray, rather than chilling thetray in advance. This alternative may accelerate initial crosslinking ascompared to using a chilled tray. Pouring onto a tray above the freezetemperature also allows the liquid mixture solution to self-level,resulting in a more uniform thickness.

At step 126, the combined precursor solutions (and/or at least partiallycrosslinked hydrogel material) may be cooled to a freezing temperature,i.e., below the freezing point of the combined precursor solutions, tofreeze the combined precursor solutions and/or hydrogel material. Forexample, the tray may be placed in a controlled cold environment, e.g.,a cold room or cold chamber, or on a temperature-controlled plate orother surface, thereby maintaining the tray at the freezing temperaturefor a predetermined time sufficient to freeze the combined precursorsolutions.

Alternatively, the tray may be exposed to a freezing medium such asliquid nitrogen, which may freeze the combined solutions relativelyquickly, or exposed to a freezing medium such as a dry ice and acetonesolution for a predetermined time period. For example, the combinedsolutions may be “snap frozen,” i.e., exposed to a freezing temperaturesufficiently low to cause the temperature of the combined solutions todrop below the freezing temperature upon exposure to the freezingmedium. Snap freezing may rapidly, substantially halt furthercrosslinking, while slower freezing stages may facilitate slowcrosslinking over a longer period of time before substantially haltingfurther crosslinking. If snap freezing is used, care should be taken toavoid cracks or other imperfections forming in the hydrogel material,e.g., which may occur when ice is created. During this step, the trayand hydrogel material may be maintained at substantially ambientpressures.

Optionally, if desired, at step 127, the frozen hydrogel may be held fora period of time before freeze drying, e.g., several days. This mayallow additional crosslinking to occur, albeit at a much reduced rate,which may result in a more resilient structure after conditioning.

At step 128, once the hydrogel material is substantially completelyfrozen, the tray may be transferred to a freeze drying machine and thefreeze drying process initiated. The process may include reducing thepressure within the freeze drying machine to a predetermined freezedrying vacuum (i.e., gauge pressure below ambient pressure) and/ormaintaining the temperature within the freeze drying machine at apredetermined freeze drying temperature for one or more periods of time.The freeze drying process is halted once a desired amount of moisture isremoved from the hydrogel material. The freeze drying step may becompleted at a single pressure and/or temperature setting of the freezedrying machine.

Alternatively, the freeze drying step may be completed in multiplestages during which the pressure and/or temperature are adjusted in adesired manner to achieve the desired level of moisture removal, i.e.,freeze drying of the hydrogel material. For example, during an initialstage, the tray may be maintained at a freeze drying temperaturesignificantly below the freezing point of the combined precursorsolutions, e.g., not more than about negative forty degrees Celsius(−40° C.), and at an appropriate application of vacuum pressure, e.g., avacuum of about fifty milliTorr (50 mTorr), for about ten minutes (10min.). Optionally, additional stages may be used to further control thefreeze drying of the tray contents. For example, during a second stage,the tray may be maintained at a temperature slightly below the freezingpoint of the combined precursor solutions for an extended duration.Thereafter, during a third stage, the vacuum may be maintained at aboutfifty milliTorr (50 mTorr) while the temperature is slowly increasedabove the freezing point of the combined precursor solutions., e.g., ata rate of about ten degrees Celsius per hour (10° C./hr.) for about onehundred fifty minutes (150 min).

Optionally, additional stages may be used to further freeze dry thecontents of the tray. For example, during a third stage, the tray may bemaintained at a freeze drying temperature of not more than aboutnegative twenty five degrees Celsius (−25° C.) and a vacuum of at leastabout fifty milliTorr (50 mTorr) for at least about 1,440 minutes.During a fourth stage, the temperature may again be raised, e.g., aboutten degrees Celsius per hour (10° C./hr.), for about three hundredminutes (300 min.) at fifty milliTorr (50 mTorr) vacuum. Finally, duringa fifth stage, the tray may be maintained at a temperature above themelt temperature of the combined precursor solutions for an extendedduration while maintaining the appropriate application of vacuumpressure, e.g., at a temperature of not more than about twenty fivedegrees Celsius (25° C.) and a vacuum of at least about fifty milliTorr(50 mTorr) for at least about two hundred forty minutes (240 min.)

Next, with continued reference to FIG. 3, at step 129, upon terminationof the freeze drying cycle, the freeze dried hydrogel material may besubjected to further environmental conditioning. Conditioningparameters, particularly temperature, may affect the final material withrespect to thickness, density, porosity, and/or surface texture. Forexample, the hydrogel material may be subjected to one or more of thefollowing: exposure to a controlled temperature and humidityenvironment, heat-assisted drying, exposure to an aerosolized buffersolution, vacuum assisted drying, and/or exposure to a controlled gasenvironment (argon, nitrogen, etc.). The hydrogel material may also bepassed through different humidification and drying phases ofenvironmental conditioning one or more times. For example, humidity maydrive the reaction previously stopped by freeze drying the material tocompletion.

The freeze dried hydrogel may also be exposed to ambient temperature,pressure, and/or humidity conditions for an initial period (i.e.,ambient temperatures, e.g., between about 20-25° C., ambient pressures,and/or ambient humidity, e.g., between about thirty and fifty percent(30-50%) relative humidity (“RH”) for a first conditioning duration,e.g., at least about twenty four hours (24 hrs.). Thereafter, thetemperature, pressure, and/or humidity may be increased (e.g., to atleast about thirty five degrees Celsius (35° C.) and at least aboutninety percent relative humidity (90% RH) for a second conditioningduration, e.g., at least about two hours (2 hrs.). Optionally, thehydrogel may be exposed to further conditioning stages at additionalpredetermined temperatures and/or humidities for predetermined durationsto facilitate yield of hydrogel material with desired properties andmorphology. For example, during a third stage, the hydrogel may beexposed to approximately thirty degrees Celsius (30° C.) and betweenabout 20-30% RH for about two hours (2 hrs.), and during a fourth stage,the hydrogel may be exposed to ambient conditions (about 20-25° C.) andhumidity between about 30-50% RH for at least about one hundred twentyhours (120 hrs).

During the one or more stages of conditioning, the hydrogel may completefurther crosslinking before medical use. For example, in one embodiment,upon completing conditioning, the hydrogel material substantiallycompletes crosslinking, e.g., to the extent that the hydrogel no longerhas a substantial amount of unreacted ester end groups available forfurther crosslinking.

If desired, one or more tests may be completed to confirm thatsubstantial crosslinking has occurred in a sample. For example, afluorescent dye, e.g., fluorescein (which may have three primary aminegroups that are likely to react with any unreacted ester groups in thesample), may be used to detect whether substantial unreacted reactiveester end groups remain within a sample. After applying the dye to thesample, the sample may be allowed sufficient time to react. The samplemay then be rinsed to remove any excess dye, and the sample may beexposed to ultraviolet light. If the sample includes substantialunreacted reactive ester end groups, the dye will emit fluorescent lightwhen exposed. Thus, if the sample is substantially completelycrosslinked, i.e., includes substantially no unreacted reactive esterend groups, the dye will not fluoresce substantially when the sample isexposed to ultraviolet light.

Alternatively, it may be possible for substantially completecrosslinking during the freeze drying stage. For example, a highlybranched active PEG may be mixed with trilysine, and freeze dried, e.g.,using the one or more steps described elsewhere herein. Thus, asuperabsorbent gel may be created simply by freeze drying.

Returning to FIG. 1, the freeze dried hydrogel material may then bemachined or otherwise formed into its final form, in step 130. Forexample, the hydrogel material may be removed from the tray, and thencut, cored, machined, or otherwise sectioned into multiple structures,e.g., one or more sheets, rods, tubes, and the like. In addition oralternatively, the hydrogel material may be rolled, compressed, and/orfolded into desired configurations or shapes. For example, the separatesections of the hydrogel material may be rolled, compressed, and/orfolded into a configuration that may be loaded into a delivery device orotherwise sized for introduction into a patient's body, as describedfurther below.

Exemplary Embodiment of the Process

For this example, a two polymer system is chosen. The system includes anamine terminated PEG and an ester terminated PEG. The polymercharacteristics are given below:

-   -   Amine base polymer: 8 arm star PEG polymer, 20 kiloDalton total        molecular weight    -   Ester base polymer: 4 arm star PEG polymer, 10 kiloDalton total        molecular weight.

The powder components are individually weighed to a mass that willresult in five percent (5%) of the mass of the final hydrogel ofexisting as solid polymeric material.

Next, a borate buffer is chosen to reconstitute the amine polymer, and aphosphate buffer is chosen to reconstitute the ester polymer. Themolarities and pH of these buffer solutions are chosen to optimizereactive conditions and working time of the materials afterreconstitution, e.g., based upon the characteristics given below:

Borate Buffer: Sodium borate in water for injection

-   -   Molarity=0.05M    -   pH=7.63±0.05

Phosphate Buffer: Sodium phosphate in water for injection

-   -   Molarity=0.01M    -   pH=4.0±0.05.        Next, the PEG-amine is reconstituted with the borate buffer, and        the PEG-ester is reconstituted with the phosphate buffer. The        precursor solutions are then combined together, e.g., in a        centrifuge tube and vigorously mixed, e.g. using a vortex        machine, for about fifteen seconds (15 sec.).

Next, one or more trays or other containers with desiredgeometry/dimensions and surface coating/coatings, e.g., including a PTFEcoating, may be chosen. The tray(s) may be readied for receiving thehydrogel precursor solutions by pre-chilling the tray(s) on the freezedry machine shelf, which may be set to a predetermined freezingtemperature. In an exemplary method, the tray area may be approximatelyfive centimeters by five centimeters (5 cm×5 cm). The tray is chilled toabout negative forty degrees Celsius (−40° C.) before use by allowing itto equilibrate on the shelf of the freeze drying machine.

Upon reaching the desired amount of crosslinking, a desired volume ofthe mixed precursor solutions is combined and allowed to reach thedesired crosslinking, e.g. ninety seconds (90 sec) to achieve twentyfive percent (25%) crosslinking with a six minute (6 min) solution, atwhich time about eight milliliters (8 ml) is then poured onto thechilled tray as it sits on the shelf of the freeze drying machine.

Immediately after the precursor solutions are poured onto the tray, thedoor to the freeze drying machine is sealed. The solutions are kept atthis temperature for a minimum of two minutes (2 min). At this point,the freeze drying cycle is initiated. Typical freeze drying parametersknown in the art may be employed such that the free and bound water areremoved without causing substantial melt back of the polymer material.Exemplary parameters for freeze drying are listed below:

Condenser Temperature Vacuum Time Step Shelf Temperature (° C.) (mTorr)(min) 1 Hold at −40° C. −50 50 10 2 Ramp temp at +10° −50 50 150 C./hour3 −25 C −50 50 1440 4 Ramp temp at +10° −50 50 300 C./hour 5 25° C. −5050 240

Upon completing the freeze drying cycle, the crosslinked material issubjected to further environmental conditioning. Exemplary conditioningparameters are listed below:

Step Time (hours) Parameters 1 ≧24 hours Ambient conditions (~20–25° C.,~30–50% RH) 2 2 hours 35° C., 90% RH 3 2 hours 30° C., ~20–30% RH 4 ≧120hours Ambient conditions (~20–25° C., ~30–50% RH)

The environmental parameters (temperature, pressure and/or humidity) towhich the hydrogel is exposed may be adjusted, e.g., to change theoutput performance of the final freeze dried material relative to rateof hydration, magnitude of volume expansion, and post production shelflife, as explained elsewhere herein. Generally, upon completing theseconditioning steps, the hydrogel material will be fully crosslinked tothe extent that the hydrogel no longer has a substantial amount ofunreacted ester end groups available for further crosslinking.

The freeze dried hydrogel is then cut to desired dimensions and/or mass.For example, the hydrogel may be formed into a size of about fifteenmillimeters long by about six to eight millimeters wide by about one toone and a half millimeters thick (15 mm×6-10 mm×1.0-1.5 mm) with atarget mass of about twenty milligrams (20 mg±6 mg). The material isthen ready to be further processed for the desired medical application.

The resulting material may be formed into one or more structures forintroduction and/or implantation into a body. The structures may beintroduced into a body alone or as part of other devices for a varietyof applications, e.g., through existing passages (e.g., blood vessels orother body lumens) or surgically created passages (e.g., punctures orother tracts through tissue), applied to biological surfaces, and thelike. For example, the structures may be used for access site closure,embolic applications, e.g., to close or isolate arterio-venousmalformations, aneurysms, tumor sites, and the like. The structures maybe incorporated into other devices, e.g., to provide coatings on stents,neurovascular coils, drug delivery implants, or other implantabledevices. The structures may also be incorporated into hemostatic patchesor other devices that may be applied to surfaces within a body. Thedevices may be permanent or may be bioaborbable such that the hydrogeland/or other components of the devices may be absorbed by the body overtime. Exemplary devices and applications that may incorporated themethods and materials described herein are disclosed in U.S. Pat. No.6,605,294, the entire disclosure of which is expressly incorporated byreference herein.

Turning to FIG. 4, an exemplary device or structure 4 is shown that maybe formed from freeze dried hydrogel material, such as those resultingfrom the methods described above. For example, the structure 4 may be aplug or other hemostatic device that may be delivered into a puncture orother body lumen to substantially seal the body lumen.

To form the structure 4, a sheet or other section of hydrogel materialcut from a larger portion may be rolled into a cylindrical shape havingfirst and second ends 6, 8. The sheet may be rolled such that thestructure 4 includes a central lumen 10 extending between the first andsecond ends 6, 8. For example, the sheet may be rolled such thatlongitudinal side edges 12, 14 of the sheet overlap one another, asshown. Alternatively, the side edges 12, 14 may be butted or connectedto one another.

In a further alternative, the section may be rolled, machined, orotherwise formed into a solid rod or bar. If desired, a central lumenmay be formed through such a rod or bar, e.g., by drilling, coring, andthe like. In addition or alternatively, the section of hydrogel (whetherrolled or not) may be compressed to provide a desired diameter or othercross-section. In exemplary embodiments, the resulting structure 4 mayhave a diameter between about 1.5-2.4 millimeters and/or a lengthbetween about thirteen to seventeen millimeters (13-17 mm). The lumen 10may have a diameter between about 0.5-0.9 mm.

Optionally, the structure 4 may include one or more components toprovide an adherent layer around the structure 4, e.g., one or moreadherent layer precursors. In addition or alternatively, the adherentlayer precursors may be infused or otherwise intermixed substantiallythroughout the structure 4. Additional information on such adherentlayers may be found in application Ser. No. 10/982,387, filed Nov. 5,2004, Ser. No. 10/982,384, and filed Nov. 5, 2004, the entiredisclosures of which are expressly incorporated by reference herein.

In addition or alternatively, the structure 4 may include pro-thromboticmaterial, e.g., including one or more biological pro-thrombotics, suchas collagen, fibrin, thrombin, carboxymethylcellulose, oxidizedcellulose, alginates, gelatin, or other protein-based material, and/orsynthetic materials, such as polyglycolic acids (PGA's ), polyactides(PLA's ), polyvinyl alcohol, and the like. Optionally, the structure 4may include therapeutic and/or pharmaceutical agents, e.g., to treatparticular disease conditions, promote healing, prevent infection and/orother adverse medical events, and the like. Such agents may be embeddedin the material of the structure 4 after forming and/or applied as oneor more coatings or layers. These agents may also be introduced eitherin the hydrogel fabrication process, e.g., to the powders beforereconstitution, to the precursor solutions at the time of mixing, to thehydrogel cake at the time of conditioning, or at any time before itsmedical use.

Optionally, the structure 4 may include an agent for increasing the rateof uptake of a solution into the freeze dried hydrogel, e.g. to reducesurface tension of the pores and/or enhance closure efficacy. Suchagents may be embedded in the material of the structure 4 after formingand/or applied as one or more coatings or layers. These agents may alsobe introduced either in the hydrogel fabrication process, e.g. to thepowders prior to reconstitution, to the precursor solutions at the timeof mixing, to the hydrogel cake at the time of conditioning, or any timebefore its medical use.

Optionally, the structure 4 may include a radiopaque agent to facilitatevisualization of the hydrogel material under x-ray or commonly usedfluoroscopic equipment. Such agents may be embedded in the material ofthe structure 4 after forming and/or applied as one or more coatings orlayers. These agents may also be introduced either in the hydrogelfabrication process, e.g. to the powders prior to reconstitution, to theprecursor solutions at the time of mixing, to the hydrogel cake at thetime of conditioning, or any time before its medical use.

In another alternative, the structure 4 may be formed from a compositeor laminate structure including two or more layers of hydrogel material(not shown). For example, each of the layers of hydrogel material may beformed as described above and laminated, molded, or otherwise formedtogether. Alternatively, a hydrogel material for a first layer may bepoured or otherwise delivered onto a tray or other container, similar tothe methods described elsewhere herein. The hydrogel material may bepoured onto the tray in a liquid or fluid state such that it adopts theshape of or at least partially fills the tray. Before completingcrosslinking of the hydrogel material, a second hydrogel material may bepoured over the first layer to create a second layer over the firstlayer. The second layer may slightly penetrate into the first hydrogellayer, e.g., to enhance bonding or otherwise laminate the two layers.

The material for the second layer may be different from the materialforming the first layer. Optionally, a third or additional layers may beapplied over the second layer. In this regard, multiple distincthydrogel layers may be created to form a laminate structure.

Before completing crosslinking of the second and/or additional layers,the tray may be frozen and then freeze dried, similar to the methodsdescribed elsewhere herein. The laminate may then be removed from thetray and shaped into a desired geometry, also as described elsewhereherein.

In yet another alternative, the hydrogel may modified with a blockingagent that substantially limits or prevents the hydrogel from swelling.The blocking agent may be transient in that it is removed via diffusionor in a fluid flow field allowing for consistent and delayed swelling asmight be needed for medical applications that require repositioning orretrievability before permanent implantation and/or disconnection from adelivery device.

Turning to FIG. 5, a delivery cartridge, catheter, or other apparatus 30may be provided for delivering the structure 4 of FIG. 4 (or otherconfiguration for the structure 4), e.g., for sealing a puncture orother body lumen. Generally, the apparatus 30 may include a deliverysheath or other tubular member 40, a plunger or other pusher member 50,and, optionally, a positioning member 60.

The delivery sheath 40 may be a substantially rigid, semi-rigid, orflexible member including a proximal end 42, a distal end 44 sized forintroduction into a body lumen or other passage through tissue, and alumen 46 sized to receive or otherwise carry the structure 4 therein.The distal end 44 may be tapered and/or may include a substantiallyatraumatic tip to facilitate advancement through a tissue passage. Thedelivery sheath 40 may include a handle (not shown), and/or one or moreseals, e.g., a hemostatic seal (also not shown), on the proximal end 42.The structure 4 may be disposed within the lumen 46, e.g., adjacent thedistal end 44. The lumen 42 may be sized such that the structure 4 isslidable therein, e.g., able to traverse distally from the deliverysheath 40 during delivery, as described further below.

The pusher member 50 may be an elongate member, e.g., a plunger,catheter, and the like, including a proximal end 52 and a distal end 54sized for slidable insertion into the lumen 42 of the delivery sheath40. Optionally, the proximal end 52 of the pusher member 50 may includea connector (not shown) for coupling the lumen 54 of the pusher member50 to a syringe or other delivery device 70 (also not shown) fordelivering one or more fluids into or through the apparatus 30.Additional information on other components, alternative apparatus, andmethods for using them may be found in co-pending applications Ser. No.10/806,952, filed Mar. 22, 2004, and Ser. No. 10/982,384, filed Nov. 5,2004, the disclosures of which are expressly incorporated by referenceherein.

Still referring to FIG. 5, the distal end 54 of the pusher member 50 maybe substantially blunt to facilitate contacting, tamping, pushing,and/or “cinching” the structure 4 within the delivery sheath 40 and/or apassage, as described further below. The pusher member 50 may besubstantially rigid, semi-rigid, and/or substantially flexible, havingsufficient column strength to allow movement of the delivery sheath 40relative to the structure 4 without buckling the pusher member 50. Inone embodiment, the pusher member 50 has sufficient column strength totamp down the structure 4 but retains a flexible or “floppy” distal end52 to prevent accidental advancement of the structure 4 into a vessel orother body lumen 94. The pusher member 50 may also include a lumen 56extending between the proximal end 52 and the distal end 54, e.g., toaccommodate the positioning member 60 and/or a guidewire (not shown).

Optionally, as in the embodiment shown in FIG. 5, the positioning member60 is a solid or hollow elongate body, including a proximal end 62, adistal end 64, and a positioning element 66 on the distal end 64. Thepositioning element 66 may be an expandable element, such as a balloon,a wire mesh structure, an expandable frame, and the like, such as thosedisclosed in application Ser. No. 10/982,384, incorporated by referenceabove. The positioning element 66 may be selectively expanded orotherwise actuated from the proximal end 62 of the positioning member60, e.g., using a source of inflation media, a pullwire, and/or otheractuator (not shown). For example, a syringe or other source ofinflation media may be coupled to a lumen (not shown) extending throughthe positioning member 60 to an inflatable positioning element.Additional information on expandable structures that may be incorporatedinto positioning member 60 may be found in U.S. Pat. Nos. 6,238,412 and6,635,068, in co-pending applications Ser. No. 10/143,514, published asPublication No. US 2003/0078616 A1, and Ser. No. 10/454,362, filed Jun.4, 2003, Ser. No. 10/806,927, filed Mar. 22, 2004, Ser. No. 10/928,744,filed Aug. 27, 2004, and Ser. No. 11/112,971, filed Apr. 22, 2005. Theentire disclosures of these references are expressly incorporated hereinby reference.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the scope ofthe appended claims.

1. A method for making superabsorbent hydrogel, comprising: forming amixture by combining precursor components to initiate crosslinking ofthe precursor components; freezing the mixture before crosslinking iscomplete; and freeze drying the mixture to form the hydrogel.
 2. Themethod of claim 1, further comprising conditioning the hydrogel afterfreeze drying.
 3. The method of claim 1, wherein the precursorcomponents comprise a first electrophilic precursor and a secondnucleophilic precursor.
 4. The method of claim 2, wherein the hydrogelsubstantially completes crosslinking when the hydrogel is conditioned.5. The method of claim 4, wherein the hydrogel has substantially nounreacted reactive ester end groups after the hydrogel is conditioned.6. The method of claim 1, further comprising placing the combinedprecursor components onto a chilled tray or container before freezingthe mixture.
 7. The method of claim 6, wherein the mixture is frozen onthe tray or container.
 8. The method of claim 6, further comprisingforming the freeze dried hydrogel into one or more structures.
 9. Themethod of claim 8, wherein the one or more structures are formed by atleast one of cutting, machining, rolling, coring, and compressing thehydrogel.
 10. The method of claim 8, wherein the one or more structurescomprise a structure that is sized for introduction into a body lumen.11. The method of claim 1, wherein crosslinking of the precursorcomponents is initiated in an aqueous phase.
 12. The method of claim 1,wherein crosslinking of the precursor components comprises covalentcrosslinking.
 13. The method of claim 1, wherein the hydrogelsubstantially completes crosslinking when the mixture is freeze dried.14. The method of claim 1, wherein the precursor components comprise ahighly branched active PEG.
 15. The method of claim 14, wherein theprecursor components further comprise an oligopeptide with two or morelysine groups.
 16. A method for making hydrogel, comprising: combiningprecursor components to initiate crosslinking of the precursorcomponents to form a hydrogel; placing the hydrogel onto a tray orcontainer chilled below the freezing point of the combined precursorcomponents; freezing the hydrogel before crosslinking is complete;freeze drying the frozen hydrogel; and conditioning the freeze driedhydrogel to substantially complete crosslinking of the precursorcomponents.
 17. The method of claim 16, further comprising forming thehydrogel into one or more structures.
 18. The method of claim 16,wherein the hydrogel is placed onto the tray or container beforecrosslinking is complete.
 19. The method of claim 16, wherein thehydrogel is placed onto the tray or container after a predeterminedamount of crosslinking has occurred.
 20. The method of claim 16, whereinthe hydrogel is placed onto the tray or container immediately uponcombining the precursor components, and wherein the hydrogel ismaintained on the tray or container at a predetermined temperature untila predetermined percentage of complete crosslinking is achieved,whereupon the hydrogel is freeze dried.
 21. The method of claim 16,wherein conditioning the hydrogel comprises one or more conditioningsteps selected from the group comprising: exposing the hydrogel to acontrolled-humidity environment; further drying the hydrogel using heat;exposing the hydrogel to a controlled gas environment; exposing thehydrogel to an aerosolized buffer solution; and desiccating thehydrogel.
 22. The method of claim 21, wherein the hydrogel isconditioned using multiple successive stages, each stage comprising oneor more of the conditioning steps.
 23. The method of claim 16, whereinthe step of freeze drying the hydrogel comprises: a first stagecomprising exposing the hydrogel to a freeze drying temperature and avacuum; and a second stage comprising at least one of increasing thefreeze drying temperature, and reducing the vacuum.
 24. The method ofclaim 23, wherein the second stage comprises reducing the vacuum for asecond stage duration, and wherein the freeze drying temperature isincreased at least intermittently during the second stage duration. 25.The method of claim 24, wherein the freeze drying temperature isincreased at a steady rate during the second stage duration.
 26. Themethod of claim 16, wherein the hydrogel substantially completescrosslinking when the hydrogel is conditioned.
 27. The method of claim26, wherein the hydrogel has substantially no unreacted reactive esterend groups after the hydrogel is conditioned.
 28. A method fordepositing a material within a patient's body, comprising: making afreeze dried hydrogel according to the method of claim 1; andintroducing the freeze dried hydrogel into the patient's body.
 29. Themethod of claim 28, wherein introducing the freeze dried hydrogelcomprises introducing the freeze dried hydrogel into a passage withinthe patient's body.
 30. The method of claim 28, wherein the passagecomprises a puncture through tissue.
 31. The method of claim 28, whereinthe passage comprises a body lumen.
 32. An implant sized forintroduction into a patient's body, comprising a hydrogel formed by themethod of claim
 1. 33. The implant of claim 32, wherein the hydrogelcomprises an open-cell hydrogel.
 34. The implant of claim 32, whereinthe hydrogel comprises at least one macromolecular species.
 35. Theimplant of claim 32, wherein the precursor components comprise PEG. 36.The implant of claim 32, wherein the precursor components comprise ahighly branched active PEG.
 37. The implant of claim 36, wherein theprecursor components further comprise an oligopeptide with two or morelysine groups.
 38. The implant of claim 32, wherein the precursorcomponents comprise a first electrophilic precursor and a secondnucleophilic precursor.
 39. The implant of claim 32, wherein thehydrogel comprises at least one polymeric species.
 40. The implant ofclaim 32, wherein the hydrogel is degradable when implanted within apatient's body.
 41. The implant of claim 32, wherein the hydrogel issubstantially non-degradable when implanted within a patient's body. 42.The implant of claim 32, wherein the hydrogel is degradable byhydrolysis.
 43. The implant of claim 32, wherein the hydrogel has adensity between 0.05 and 0.30 grams per cubic centimeter (g/cc).
 44. Theimplant of claim 32, wherein the hydrogel has a rate of magnitude ofexpansion between about five and fifty (5-50) times the initial volumewhen exposed to an aqueous environment.
 45. The implant of claim 32,wherein the hydrogel has a rate of swelling such that, when exposed toan aqueous environment, the hydrogel expands between about five hundredand three thousand percent (500-3000%) of the initial mass within aboutfive to sixty (5-60) seconds.